An article, such as bank note, identity document and negotiable securities, is vulnerable to simulation and counterfeit due to its high added value. Optical anti-counterfeiting technologies (e.g., holography, optical variability and micro-lens array) are widely applied to facilitate the general public identify authenticity of the document with high added value and resist the reproduction thereof performed by means of the current digital-technology.
The micro-lens array anti-counterfeiting technology is applied to perform sampling on the corresponding micro image by utilizing the micro-lens as a micro-sampling tool, it may manifest a dynamic and magnified image which has animation effects and is visible for human eyes by means of designing sampling points under different viewing angles. The animation effects comprises orthogonal dynamic, sink, float, three-dimensional sense, rotation, scaling, dual channel, and likes (please refer to patent document US2008/0036196A1). When the micro-lens array anti-counterfeiting technology is specifically applied, it may be combined with the technology of Moire magnifiers (see article: “Properties of moire magnifiers”, Hala Kamal, Reinhard Volkel and Javier Alda, Optical Engineering, Vol. 37, No. 11, pp 3007-3014, publicized on November 1998), and a plurality of above animation effects are generated by means of periodically arranged micro-lens (i.e., a micro-sampling tool) and a micro image which is periodically arranged and having a period which is similar with that of the micro-lens, wherein the micro image is located near the focal point of said micro-lens.
The micro image and the background shall have sufficient contrast such that they can be easily identified under a variety of environments, that is, it is necessary to colorize the micro image. Given that the structure of desirable micro image is very fine (about a few microns), such an accuracy grade is unreachable by utilizing a general printing technology. There are two colorizing methods at present, one method is disclosed in patent documents (e.g., CN1906547A) as follows: forming grooves with a certain depth in the micro image region, filling the grooves with ink by means of the blade coating processes, and the excessive materials which are located beyond the micro image region shall be substantially removed. In order to obtain a favorable colorizing effect, this method is significantly restrictive on the width of lines and depth of grooves of the micro image as well as matching relationship therebetween. Another method is applied based on the micro-nano structure, for instance, patent document US20030179364 discloses a solution of performing a black colorization of the micro image by means of an optical absorbing structure with a high width-to-depth ratio, and the patent document US20100307705A1 discloses a solution of performing a colorization on the micro image by filling with nanoparticles or benched metallic nanostructure.
However, the above-mentioned colorizing methods can hardly reach a colorful tinting, or can hardly be applied in the production (for example, the benched structure and the manner that the coating only covers the flat surface of micro image).